单项选择题
A．nobody will try to get them B．they can become very valuable C．everybody would like to buy them D．they will be worthless
A．When a child is two years old, he prefers to use both of his hands to grasp objects. B．Scientists have given the reason for this tendency. C．A monkey can use both of his hands equally well. D．Those who prefer to use their left hands live a difficult lif
A. is able to design new tools B. measures the amount of energy used C. enables people to see the muscular movements D. visualizes electrical signals